Messages in this thread | | | Date | Tue, 08 Feb 2011 11:15:56 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH] KVM: x86: Convert tsc_write_lock to raw_spinlock |
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On 02/07/2011 07:23 PM, Jan Kiszka wrote: > On 2011-02-07 18:10, Avi Kivity wrote: > > On 02/07/2011 06:59 PM, Jan Kiszka wrote: > >>> > >>> (well, actually, cpufreq_notifier and kvm_arch_hardware_enable are > >>> already non preemptible, and the stats code should just go away?) > >> > >> The stats code is trivial to convert, so it doesn't matter. > > > > Removal is easier. > > Is that stat interface no longer used?
It's there for compatibility. I'm itching to remove it. See qemu-kvm.git/kvm/kvm_stat for the only known user, and for the replacement via tracepoints.
Tracepoints have marginally lower overhead when disabled, and somewhat higher overhead when enabled. A disadvantage of tracepoints is that it is harder to associate an event with a vm when that event is triggered by a workqueue, but I don't think it matters in practice (kvm_stat doesn't even provide a per-vm breakdown).
> > > >> But what about mmu_shrink and its list_move_tail? How is this > >> synchronized against kvm_destroy_vm - already today? > > > > kvm_destroy_vm() takes kvm_lock. If a vm is destroyed before > > mmu_shrink(), mmu_shrink() will never see it. If we reach mmu_shrink() > > before kvm_destroy_vm(), the latter will wait until mmu_shrink() is done. > > > > Ah, I was confused. Would require some more logic if we wanted to make > the loop lock-less, though.
Yes, the usual rcu_read_lock() / grab reference / rcu_read_unlock().
-- error compiling committee.c: too many arguments to function
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